Process for applying stress-balanced coating composite to dielectric surface of gas discharge device

ABSTRACT

There is disclosed a process for applying a stress-balanced coating composite to each dielectric surface of a multiple gaseous discharge display/memory panel having an electrical memory and capable of producing a visual display, the panel being characterized by an ionizable gaseous medium in a gas chamber formed by a pair of opposed dielectric material charge storage members, each of which is respectively backed by an array of electrodes, the electrodes behind each dielectric material member being oriented with respect to the electrodes behind the opposing dielectric material member so as to define a plurality of discrete discharge volumes constituting a discharge unit. The surface of each dielectric material charge storage member is selectively coated with a first layer of at least one compound of Group IIA, Al, Si, Ti, Zr, Hf, or mixtures thereof; a second layer of at least one compound of Group IIA, Al, Si, Ti, Zr, Hf, or mixtures thereof which is chemically different from the first layer; and a third layer of an electron-emissive material; the combination of the first and second layers being sufficient to prevent ion migration from the dielectric to the third layer and sufficient to provide a thermally and structurally stable base for the third layer; and the second layer being chemically inert relative to the third layer.

Wit tes Patent [1 1 Ernsthausen et al.

[ Sept. 17, 1974 PROCESS FOR APPLYING STRESS-BALANCED COATHNG COMPOSITET0 DHELECTRHC SURFACE 01* GAS DISCHARGE DEVICE [75] Inventors: Roger E.Ernsthausen, Luckey;

Brooke R. Emch, Toledo, both of Ohio [73] Assignee: Owens-1111110115,Inc, Toledo, Ohio [22] Filed: July 14, 1971 21 Appl. No.: 162,638

[52] US. Cl 1117/217, l17/DIG. 12, 117/106 R, 117/211, 117/215, 117/219,117/221,

[51] Int. Cl B44d ll/l8, B44d 1/16 58 Field 61 Search 117/219, 217, 106,221, a,

H 1 17/222,223, 229, 211, 224; 313/220,221,1ss

Primary Examiner-Cameron K. Weiffenbach Attorney, Agent, or Firm-DonaldKeith Wedding [57] ABST? There is disclosed a process for applying astressbalanced coating composite to each dielectric surface of amultiple gaseous discharge display/memory panel having an electricalmemory and capable of producing a visual display, the panel beingcharacterized by an ionizable gaseous medium in a gas chamber formed bya pair of opposed dielectric material charge storage members, each ofwhich is respectively backed by an array of electrodes, the electrodesbehind each dielectric material member being oriented with respect tothe electrodes behind the opposing dielectric material member so as todefine a plurality of discrete discharge volumes constituting adischarge unit.

The surface of each dielectric material charge storage member isselectively coated with a first layer of at least one compound of Group11A, Al, Si, Ti, Zr, Hf, or mixtures thereof; a second layer of at leastone compound of Group lIA, Al, Si, Ti, Zr, Hf, or mixtures thereof whichis chemically different from the first layer; and a third layer of anelectron-emissive material; the combination of the first and secondlayers being sufficient to prevent ion migration from the dielectric tothe third layer and sufficient to provide a thermally and structurallystable base for the third layer; and the second layer being chemicallyinert relative to the third layer.

39 Claims, 6 Drawing Figures PROCESS FOR APPLYllNG STRESS-BALANCEDCOATING COMPOSITE TO DIELECTRIC SURFACE OE GAS DISCHARGE DEVICE THEINVENTION This invention relates to novel multiple gas dischargedisplay/memory panels or units which have an electrical memory and whichare capable of producing a visual display or representation of data suchas numerals, letters, television display, radar displays, binary words,etc.

Multiple gas discharge display and/or memory panels of the type withwhich the present invention is concemed are characterized by anionizable gaseous medium, usually a mixture of at least two gases at anappropriate gas pressure, in a thin gas chamber or space between a pairof opposed dielectric charge storage members which are backed byconductor (electrode) members, the conductor members backing eachdielectric member typically being transversely oriented to define aplurality of discrete discharge volumes and constituting a dischargeunit. In some prior art panels the discharge units are additionallydefined by surrounding or confining physical structure such as by cellsor apertures in perforated glass plates and the like so as to bephysically isolated relative to other units.

In either case, with or without the confining physical structure,charges (electrons, ions) produced upon ionization of the gas of aselected discharge unit, when proper alternating operating potentialsare applied to selected conductors thereof, are collected upon thesurfaces of the dielectric at specifically defined loca tions andconstitute an electrical field opposing the electrical field whichcreated them so as to terminate the discharge for the remainder of thehalf cycle and aid in the initiation of a discharge on a succeedingopposite half cycle of applied voltage, such charges as are storedconstituting an electrical memory.

Thus, thedielectric layers prevent the passage of any conductive currentfrom the conductor members to the gaseous medium and also serve ascollecting surfaces for ionized gaseous medium charges (electrons, ions)during the alternate half cycles of the AC. operating potentials, suchcharges collecting first on one elemental or discrete dielectric surfacearea and then on an opposing elemental or discrete dielectric surfacearea on alternate half cycles to constitute an electrical mem- Anexample of a panel structure containing nonphysically isolated or opendischarge units is disclosed in U.S. Pat. No. 3,499,167 issued toTheodore C. Baker et al.

An example of a panel containing physically isolated units is disclosedin the article by D. L. Bitzer and H. G. Slottow entitled The PlasmaDisplay Panel A Digitally Addressable Display With Inherent Memory,Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco,Calif, Nov. 1966, pages 541-547. Also reference is made to U.S. Pat. No.3,559,190 to Bitzer et al.

In the operation of the panel, a continuous volume of ionizable gas isconfined between a pair of dielectric surfaces backed by conductorarrays forming matrix elements. The cross conductor arrays may beorthogonally related (but any other configuration of conductor arraysmay be used) to define a plurality of opposed pairs of charge storageareas on the surfaces of the dielectric bounding or confining the gas.Thus, for a conductor matrix having H rows and C columns the number ofelemental discharge volumes will be the-product H X C and the number ofelemental or discrete areas will be twice the number of elementaldischarge volumes.

In addition to the matrix configuration, the conductor arrays may beshaped otherwise. Accordingly, while the preferred conductor arrangementis of the crossed grid type as shown herein, it is likewise apparentthat where an infinite variety of two dimentional display patterns arenot necessary, as where specific standardized visual shapes (e.g.,numerals, letters, words, etc.) are to be formed and image resolution isnot critical, the conductors may be shaped accordingly.

The gas is one which produces light (if visual display is an objective)and a copious supply of charges (ions.

and electrons) during discharge. In an open cell Baker et al. typepanel, the gas pressure and the electric field are sufficient tolaterally confine charges generated on discharge within elemental ordiscrete volumes of gas between opposed pairs of elemental or discretedielectric areas within the perimeter of such areas, especially in apanel containing non-isolated units.

As described in the Baker et al. patent, the space between thedielectric surfaces occupied by the gas is such as to permit photonsgenerated on discharge in a selected discrete or elemental volume of gasto pass freely through the gas space and strike surface areas ofdielectric remote from the selected discrete volumes, such remote,photon struck dielectric surface areas thereby emitting electrons so asto condition other and more remote elemental volumes for discharges at auniform applied potential.

With respect to the memory function of a given discharge panel, theallowable distance or spacing between the dielectric surfaces depends,inter alia, on the frequency of the alternating current supply, thedistance typically being greater for lower frequencies.

While the prior art does disclose gaseous discharge devices havingexternally positioned electrodes for initiating a gaseous discharge,sometimes called electrodeless discharges, such prior art devicesutilize frequencies and spacings or discharge volumes and operatingpressures such that although discharges are initiated in the gaseousmedium, such discharges are ineffective or not utilized for chargegeneration and storage at higher frequencies; although charge storagemay be realized at lower frequencies, such charge storage has not beenutilized in a display/memory device in the manner of the Bitzer-Slottowor Baker et al. inventions.

The term memory margin is defined herein as M.M. (V ENV where V is thehalf amplitude of the smallest sustaining voltage signal which resultsin a discharge every half cycle, but at which the cell is not bi'stableand V is the half amplitude of the minimum applied voltage sufficient tosustain discharges once initiated.

It will be understood that basic electrical phenomena utilized in thisinvention is the generation of charges (ions and electrons) alternatelystorable at pairs of opposed or facing discrete points or areas on apair of dielectric surfaces backed by conductors connected to a sourceof operating potential. Such stored charges result in an electricalfield opposing the field produced by the applied potential that createdthem and hence operate to terminate ionization in the elemental gasvolume between opposed or facing discrete points or areas of dielectricsurface. The term sustain a discharge means producing a sequence ofmomentary discharges, one discharge for each half cycle of appliedalternating sustaining voltage, once the elemental gas volume has beenfired, to maintain alternate storing of charges at pairs of opposeddiscrete areas on the dielectric surfaces.

The features and advantages of the invention will be better understoodby reference to the following detailed description when considered inconnection with the accompanying drawings.

FIGS. 1-4 and the description of these figures are from the abovementioned Baker et al. U.S. Pat. No. 3,499,167.

FIG. 1 is a partially cut-away plan view of a gaseous display/memorypanel as connected to a diagrammatically illustrated source of operatingpotentials,

FIG. 2 is a cross-sectional view (enlarged, but not to proportionalscale since the thickness of the gas volume dielectric members andconductor arrays have been enlarged for purposes of illustration) takenon the lines 22 of FIG. 1,

FIG. 3 is an explanatory partial cross-sectional view similar to FIG. 1(enlarged, but not to proportional scale),

FIG. 4 is an isometric view of a larger gaseous discharge display/memorypanel, and

FIGS. 5 and 6 are explanatory partial cross-sectional views similar toFIG. 3 showing different embodiments of the present invention.

The invention utilizes a pair of dielectric films or coatings 10 and 11separated by a thin layer or volume of a gaseous discharge medium 12,said medium 12 producing a copious supply of charges (ions andelectrons) which are alternately collectable on the surfaces of thedielectric members at opposed or facing elemental or discrete areas Xand Y defined by the conductor matrix on nongas-contacting sides of thedielectric members, each dielectric member presenting large open surfaceareas and a plurality of pairs of elemental X and Y areas. While theelectrically operative structural members such as the dielectric members10 and 11 and conductor matrixes I3 and 14 are all relatively thin(being exaggerated in thickness in the drawings) they are formed on andsupported by rigid nonconductive support members 16 and 17 respectively.

Preferably, one or both of nonconductive support members 16 and 17 passlight produced by discharge in the elemental gas volumes. Preferably,they are transparent glass members and these members essentially definethe overall thickness and strength of the panel. For example, thethickness of gas layer 12 as determined by spacer 15 is under 10 milsand preferably about 5 to 6 mils, dielectric layers 10 and 11 (over theconductors at the elemental or discrete X and Y areas) is between I and2 mils thick, and conductors l3 and 14 about 8,000 angstroms thick (tinoxide). However, support members 16 and 17 are much thicker(particularly larger panels) so as to provide as much ruggedness as maybe desired to compensate for stresses in the panel. Support members 16and 17 also serve as heat sinks for heat generated by discharges andthus minimize the effect of temperature on operation of the device. Ifit is desired that only the memory function be utilized, then none ofthe members need be transparent to light although for purposes describedlater herein it is preferred that one of the support members and membersformed thereon be transparent to or pass ultraviolet radiation.

Except for being nonconductive or good insulators the electricalproperties of support members 16 and 17 are not critical. The mainfunction of support members 16' and I7 is to provide mechanical supportand strength for the entire panel, particularly with respect to pressuredifferential acting on the panel and thermal shock. As noted earlier,they should have thermal expansion characteristics substantiallymatching the thermal expansion characteristics of dielectric layers 10and 11. Ordinary inch commercial grade soda lime plate glasses have beenused for this purpose. Other glasses such as low expansion glasses ortransparent devitrified glasses can be used provided they can withstandprocessing and have expansion characteristics substantially matchingexpansion characteristics of the dielectric coatings l0 and 11. Forgiven pressure differentials and thickness of plates the stress anddeflection of plates may be determined by following standard stress andstrain formulas (see R. J. Roark, Formulas for Stress and Strain,McGraw-Hill, 1954).

Spacer 15 may be made of the same glass material as dielectric films 10and 11 and may be an integral rib formed on one of the dielectricmembers and fused to the other members to form a bakeable hermetic sealenclosing and confining the ionizable gas volume 12. However, a separatefinal hermetic seal may be effected by a high strength devitrified glasssealant 15S. Tubulation I8 is provided for exhausting the space betweendielectric members 10 and 11 and filling the space with the volume ofionizable gas. For large panels small bead like solder glass spacerssuch as shown at 15B may be located between conductors intersections andfused to dielectric members 10 and II to aid in withstanding stress onthe panel and maintain uniformity of thickness of gas volume 12.

Conductor arrays I3 and 14 may be formed on support members 16 and 17 bya number of well known processes, such as photoetching, vacuumdeposition, stencil screening, etc. In the panel shown in FIG. 4, thecenter to center spacing of conductors in the respective arrays is about30 mils. Transparent or semitransparent conductive material such as tinoxide, gold or aluminum can be used to form the conductor arrays andshould have a resistance less than 3,000 ohms per line. It is importantto select a conductor material that is not attacked during processing bythe dielectric material.

It will be appreciated that conductor arrays 13 and 14 may be wires orfilaments of copper, gold, silver or aluminum or any other conductivemetal or material. For example 1 mil wire filaments are commerciallyavailable and may be used in the invention. However, formed in situconductor arrays are preferred since they may be more easily anduniformly placed on and adhered to the support plates 16 and 17.

Dielectric layer members 10 and 11 are formed of an inorganic materialand are preferably formed in situ as an adherent film or coating whichis not chemically or physically effected during bake-out of the panel.One such material is a solder glass such as Kimble SG 68 manufactured byand commercially available from the assignee of the present invention.

This glass has thermal expansion characteristics substantially matchingthe thermal expansion characteristics of certain soda-lime glasses, andcan be used as the dielectric layer when the support members 16 and 17are soda-lime glass plates. Dielectric layers 10 and 11 must be smoothand have a dielectric strength of about l,000 v. and be electricallyhomogeneous on a microscopic scale (e.g., no cracks, bubbles, crystals,dirt, surface films, etc.). In addition, the surfaces of dielectriclayers 10 and 11 should be good photoemitters of electrons in a bakedout condition. However, a supply of free electrons for conditioning gas12 for the ionization process may be provided by inclusion of aradioactive material within the glass or gas space. A preferred range ofthickness of dielectric layers 10 and 11 overlying the conductor arrays13 and 14 is between 1 and 2 mils. f course, for an optical display atleast one of dielectric layers 10 and 11 should pass light generated ondischarge and be transparent or translucent and, preferably, both layersare optically transparent.

The preferred spacing between surfaces of the dielectric films is aboutto 6 mils with conductor arrays 13 and 14- having center to centerspacing of about 30 mils.

The ends of conductors 14-1 14- 1 and support member 17 extend beyondthe enclosed gas volume 12 and are exposed for the purpose of makingelectrical connection to interface and addressing circuitry 19.Likewise, the ends of conductors 13-1 1.3-4 on support member 16 extendbeyond the enclosed gas volume 12 and are exposed for the purpose ofmaking electrical connection to interface and addressing circuitry 19.

As in known display systems, the interface and addressing circuitry orsystem 19 may be relatively inexpensive line scan systems or thesomewhat more expensive high speed random access systems. However, it isto be noted that a lower amplitude of operating potentials helps toreduce problems associated with the interface circuitry between theaddressing system and the display/memory panel, per se. Thus, byproviding a panel having greateruniformity in the dischargecharacteristics throughout the panel, tolerances and operatingcharacteristics of the panel with which the interfacing circuitrycooperate, are made less rigid.

One mode of initiating operation of the panel will be described withreference to FIG. 3, which illustrates the condition of one elementalgas volume 30 having an elemental cross-sectional area and volume whichis quite small relative to the entire volume and cross-sectional area ofgas 12. The cross-sectional area of volume 30 is defined by theoverlapping common elemental areas of the conductor arrays and thevolume is equal to the product of the distance between the dielectricsurfaces and the elemental area. It is apparent that if the conductorarrays are uniform and linear and are orthogonally (at right angles toeach other) related each of elemental areas X and Y will be squares andif conductors of one conductor array are wider than conductors of theother conductor array, said areas will be rectangles. If the conductorarrays are at transverse angles relative to each other, other than 90,the areas will be diamond shaped so that the cross-sectional shape ofeach volume is determined solely in the first instance by the shape ofthe common area of overlap between conductors in the conductor arrays 13and 14. The dotted lines 30 are imaginary lines to show a boundary ofone elemental volume about the center of which each elemental dischargetakes place. As described earlier herein, it is known that thecross-sectional area of the discharge in a gas is affected by, interalia, the pressure of the gas, such that, if desired, the discharge mayeven be constricted to within an area smaller than the area of conductoroverlap. By utilization of this phenomena, the light production may beconfined or resolved substantially to the area of the elementalcross-sectional area defined by conductor overlap. Moreover, byoperating at such pressure charges (ions and electrons) produced ondischarge are laterally confined so as to not materially affectoperation of adjacent elemental discharge volumes.

In the instant shown in FIG. 3, a conditioning discharge about thecenter of elemental volume 30 has been initiated by application toconductor 13-1 and conductor 141-1 firing potential V, as derived from asource 35 of variable phase, for example, and source 36 of sustainingpotential V, (which. may be a sine wave, for example). The potential V,is added to the sustaining potential V, as sustaining potential Vincreases in magnitude to initiate the conditioning discharge about thecenter of elemental volume 30 shown in FIG. 3. There, the phase of thesource 35 of potential V, has been adjusted into adding relation to thealternating voltage from the source 36 of sustaining voltage V, toprovide a voltage V,,', when switch 33 has been closed, to conductors13-1 and 14-1 defining elementary gas volume 30 sufficient (in timeand/or magnitude) to produce a light generating discharge centered aboutdiscrete elemental gas volume 30. At the instant shown, since conductor13-1 is positive, electrons 32 have collected on and are moving to anelemental area of dielectric member 10 substantially corresponding tothe area of elemental gas volume 30 and the less mobile positive ions 31are beginning to collect on the opposed elemental area of dielectricmember 11 since it is negative. As these charges build up, theyconstitute a back voltage opposed to the voltage applied to conductors13-1 and 14-1 and serve to terminate the discharge in elemental gasvolume 30 for the remainder of a half cycle.

During the discharge about the center of elemental gas volume 30,photons are produced which are free to move or pass through gas medium12, as indicated by arrows 37, to strike or impact remote surface areasof photoemissive dielectric members 10 and 11, causing such remote areasto release electrons 38. Electrons 38 are, in effect, free electrons ingas medium 12 and condition each other discrete elemental gas volume foroperation at a lower firing potential V; which is lower in magnitudethan the firing potential V, for the initial discharge about the centerof elemental volume 30 and this voltage is substantially uniform foreach other elemental gas volume.

Thus, elimination of physical obstructions or barriers between discreteelemental volumes, permits photons to travel via the space occupied bythe gas medium 12 to impact remote surface areas of dielectric members10 and 11 and provides a mechanism for supplying free electrons to allelemental gas volumes, thereby conditioning all discrete elemental gasvolumes for subsequent discharges, respectively, at a uniform lowerapplied potential. While in F16. 3 a single elemental volume 30 isshown, it will be appreciated that an entire row (or column) ofelemental gas volumes may be maintained in a fired condition duringnormal operation of the device with the light produced thereby beingmasked or blocked off from the normal viewing area and not used fordisplay purposes. It can be expected that in some applications therewill always be at least one elemental volume in a fired condition andproducing light in a panel, and in such applications it is not necessaryto provide separate discharge or generation of photons for purposesdescribed earlier.

However, as described earlier, the entire gas volume can be conditionedfor operation at uniform firing potentials by use of external orinternal radiation so that there will be no need for a separate sourceof higher potential for initiating an initial discharge. Thus, byradiating the panel with ultraviolet radiation or by inclusion of aradioactive material within the glass materials or gas space, alldischarge volumes can be operated at uniform potentials from addressingand interface circuit 19.

Since each discharge is terminated upon a build up or storage of chargesat opposed pairs of elemental areas, the light produced is likewiseterminated. In fact, light production lasts for only a small fraction ofa half cycle of applied alternating potential and depending on designparameters, is in the nanosecond range.

After the initial firing or discharge of discrete elemental gas volume30 by a firing potential V,, switch 33 may be opened so that only thesustaining voltage V, from source 36 is applied to conductors 13-1 and14-1. Due to the storage of charges (e.g., the memory) at the opposedelemental areas X and Y, the elemental gas volume 30 will dischargeagain at or near the peak of negative half cycles of sustaining voltageV, to again produce a momentary pulse of light. At this time, due toreversal of field direction, electrons 32 will collect on and be storedon elemental surface area Y of dielectric member 11 and positive ions 31will collect and be stored on elemental surface area X of dielectricmember 10. After a few cycles of sustaining voltage V the times ofdischarges become symmetrically located with respect to the wave form ofsustaining voltage V,. At remote elemental volumes, as for example, theelemen- 'tal volumes defined by conductor 1.4-1 with conductors 13-2 and13-3, a uniform magnitude or potential V, from source 60 is selectivelyadded by one or both of switches 34-2 or 34-3 to the sustaining voltageV, shown as 36, to fire one or both of these elemental dischargevolumes. Due to the presence of free electrons produced as a result ofthe discharge centered about elemental volume 30, each of these remotediscrete elemental volumes have been conditioned for operation atuniform firing potential V,.

In order to turn off" an elemental gas volume (i.e., terminate asequence of discharge representing the on state), the sustaining voltagemay be removed. However, since this would also turn off" other elementalvolumes along a row or column, it is preferred that the volumes beselectively turned of by application to selected on elemental volumes avoltage which can neutralize the charges stored at the pairs of opposedelemental areas.

This can be accomplished in a number of ways, as for example, varyingthe phase or time position of the potential from source 60 to where thatvoltage combined with the potential form source 36' falls substantiallybelow the sustaining voltage.

It is apparent that the plates 16-17 need not be flat but may be curved,curvature of facing surfaces of each plate being complementary to eachother. While the preferred conductor arrangement is of the crossed gridtype as shown herein, it is likewise apparent that where an infinitevariety of two dimensional display patterns are not necessary, as wherespecific standardized visual shapes (e.g., numerals, letters, words,etc.) are to be formed and image resolution is not critical, theconductors may be shaped accordingly.

The device shown in FIG. 4 is a panel having a large number of elementalvolumes similar to elemental volume 30 (FIG. 3). In this case more roomis provided to make electrical connection to the conductor arrays 13'and 14, respectively, by extending the surfaces of support members 16'and 17' beyond scale 15S, alternate conductors being extended onalternate sides. Conductor arrays 13' and 14 as well as support members16' and 17 are transparent. The dielectric coatings are not shown inFIG. 4 but are likewise transparent so that the panel may be viewed fromeither side.

In accordance with this invention, there is provided a novel process forthe preparation of a gas discharge panel which comprises selectivelyapplying a stressbalanced, three-layer, coating composite to eachdielectric charge-storage surface of a gas discharge device.

More especially, there is provided a gas discharge display/memory panelmanufacturing process which comprises thermally evaporating anddepositing upon each dielectric material charge-storage surface acontinuous, relatively-flaw free, three-layer, stressbalanced composite.

In one particular manufacture of a gas discharge display/memory deviceand with reference to FIG. 5, each dielectric 10, 11 is applied to aglass substrate 16, 17 to which the electrode conductors 13, 14 havebeen previously applied. The dielectric layer l0, 11 is typicallyapplied directly to the electrode side of the substrate 16, 17; that is,each dielectric is applied in direct contact with and over itsrespective electrode array.

A sealing composition is appropriately applied, such as by a printingmethod, around or near the outer edge (perimeter or circumference) ofone or both substrates. The substrates are then sealed together,dielectric surface to dielectric surface. If the dielectric extends outto the edges of the substrate, the sealing composition will be on top ofthe outer surface portion of such dielectric.

In the preferred practice hereof, the three-layer composite is appliedwhile each dielectric (including any supporting substrate) is at atemperature of about F to about 600F.

In still another preferred practice hereof, the deposition of thecomposite is after the seal has been applied to one or both of thesupport substrates.

In accordance with the specific practice of this invention, there isdeposited a first layer 101, 111 of at least one compound of Group IIA,Al, Si, Ti, Zr, Hf, or mixtures thereof; a second layer 102, 112 of atleast one compound of Group IIA, Al, Si, Ti, Zr, I-If, or mixturesthereof which is chemically different from the first layer; and a thirdlayer 103, 113 of electron-emissive material; the combination of thefirst and second layers being sufficient to prevent ion migration fromthe dielectric to the third layer and sufficient to provide a thermallyand structurally stable base for the third layer; and the second layerbeing chemically inert relative to the third layer.

Typical compounds contemplated for the first and second layers includethe oxides, nitrides, fluorides, borides, and carbides of the Group IIAelements, A], Si, Ti, Zr, l-If, or mixtures thereof. By mixturesthereof, it is intended that a given layer may comprise a mixture of twoor more compounds (of the same or different element) and/or may comprisea single compound containing two or more elements.

The combination of the first and second layers should provide athermally and structurally stable base for the top layer; that is, thefirst two layers must be such that there is a minimum formation ofcracks, fissures, flaws, crazes, crevices, etc., especially during thethermal sealing of the panel.

As used herein Group HA is defined as including the elements Be, Mg, Ca,Sr, and Ba. Likewise, Ra is intended although economics may prohibitcommon usage.

The three layers are preferably non-conductive. However, conductivematerials may be utilized if such are applied in islandlike geometricpatterns so as to be structurally and electrically isolated from theelectrodes and/or gaseous medium. Fig. 6 is a crosssectional view of apanel as described in US. Pat. No. 3,559,190 to Bitzer et al. whereinperforations or cells 120 in an inner insulating member 121 physicallyisolate each discharge unit. The island-like three layers are located onthe dielectric layers l0, 11 at each cell site.

As used herein, electron-emissive refers to the processes ofphotoemission, secondary electron emission of ion and/or electronbombardment, and thermionic electron emission.

Typical conductive or semi-conductive materials which may be utilizedsuch as in an isolated geometric arrangement, comprise GaAs, GaP, InAs,InSb, InP, NiO, AgOCs, and AuOCs.

Preferably there is used a non-conductive substance such as CsF, Csl,lead oxide, and/or magnesium oxide.

In a specific embodiment of this invention, each dielectric surface isthermally evaporated and deposited with a first layer of silica, asecond layer of aluminum oxide, and a third layer of lead oxide.

In another specific embodiment, there is thermally evaporated anddeposited a first layer of silica, a second layer of zirconium oxide,and a third layer of lead oxide.

A further specific embodiment comprises the thermal evaporating anddepositing of a first layer of magnesium oxide, a second layer ofzirconium oxide, and a third layer of lead oxide.

Still another specific embodiment comprises thermally evaporating anddepositing a first layer of Si N,,, a second layer of silica, and athird layer of lead oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of magnesium oxide, a second layer of aluminum oxide, and athird layer of lead oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of silica, a second layer of aluminum oxide, and a thirdlayer of magnesium oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of silica, a second layer of zirconium oxide, and a thirdlayer of magnesium oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of magnesium oxide, a second layer of zirconium oxide, and athird layer of magnesium oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of Si N,,, a second layer of silica, and a third layer ofmagnesium oxide.

Another embodiment comprises thermally evaporating and depositing afirst layer of magnesium oxide, a second layer of aluminum oxide, and athird layer of magnesium oxide.

In accordance with this invention, the composite layers are applied by athermal evaporation and deposition process wherein a source of the layermaterial is thermally evaporated and eondensated as a thin solidcontinuous film or layer. The process is preferably done under a vacuum.

Examples of thermal evaporation, also known as physical vapordeposition, include resistive heating which comprises heating theselected material with a resistively heated filament; laser evaporation;and RF or induction heating evaporation.

One highly preferred thermal evaporation process is electron beamevaporation which comprises electron bombardment of the selectedmaterial so as to heat and evaporate it. As already noted, theevaporation and deposition are preferably under vacuum.

In the typical practice hereof, the first two layers are oxides.

In one embodiment of such practice, one or both oxide layers is applieddirectly to the surface of the dielectric material, or preceding layer,via the aforementioned processes.

In another embodiment thereof, at least one of the oxide layers isformed in situ on the dielectric surface, e.g., by applying theelemental metal or metalloid (or a source thereof) to the dielectricsurface followed by oxidation. One such in situ process comprisesapplying metal or metalloid melt to the dielectric followed by oxidationof the melt during the cooling thereof so as to form the oxide layer.Another in situ process comprises applying an oxidizable source of theelemental metal or metalloid to the surface. Typical of such oxidizablesources include minerals and/or compounds containing the metal ormetalloid, especially those organometals or organometalloids which arereadily heat decomposed or pyrolyzed.

In the usual practice hereof, each of the three layers is applied to orformed on the dielectric material surface to a thickness of at leastabout angstrom units per layer with a range of about 200 angstrom unitsper layer up to about 1 micron 10,000 angstrom units) per layer.

As used herein, the terms film or layer are intended to be all inclusiveof other similar terms such as deposit, coating, finish, spread,covering, etc.

In the fabrication of a gaseous discharge panel, the dielectric materialis typically applied to and cured on the surface of a supporting glasssubstrate or base to which the electrode or conductor elements have beenpreviously applied. The glass substrate may be of any suitablecomposition such as a soda lime glass composition. Two glass substratescontaining electrodes and cured dielectric are then appropriately heatsealed together so as to form a panel. As noted hereinbefore, in thepreferred practice of this invention, each of the three layers isapplied to the surface of the cured dielectric before the panel heatsealing cycle, with the 'dielectric and substrate at a temperature ofabout 150F to about 600F.

Gaseous discharge display/memory panels prepared in accordance with thepractice of this invention have the advantage of decreased aging cycletime, lower operating voltages, and substantially uniform operatingvoltages; that is, operating voltages which are essentially stable as afunction of total panel operating time. As used herein, voltage isdefined as any voltage required for operation of the panel includingfiring and dynamic sustaining voltages as well as any other voltagesused for manipulation of a cell discharge.

Also this invention has the further important advantage of providing agas discharge device dielectric surface which will consistently remaincontinuous and coherent through the thermal cycling required in thepanel sealing operations, that is, there results a sufficientlystress-balanced three coating composite which avoids film cracking,crazing, etc. Prior art thin films deposited at the dielectric dischargesurface possess a marked tendency to craze when subjected toconventional sealing cycles. The advantage of using an essentiallystress-balanced composite of films is that it permits conventionalsealing with commercial solder glasses. Another advantage is that thestress-balanced composite is much less sensitive to substrateimperfections and to substrate temperature during deposition.

The following examples are intended to illustrate some of the bestembodiments contemplated by the inventor in the practice of thisinvention.

EXAMPLE I Using a Mi inch thick soda-lime silicate base glass substratecontaining gold conductors and a bulk glass dielectric of about 1 milthickness, a composite of coatings is sequentially deposited by vacuumdeposition techniques using electron beam evaporation. On the bulk glassdielectric, about 700 A. of magnesium oxide is first deposited followedby a second layer of about 1,000 A. of alumina. Onto this a third layerof about 1,000 A. of lead oxide is deposited to form thedischarge-memory surface. Subsequent sealing of substrates coated inthis way with commercial solder glasses repeatedly demonstrates thethermal stability of the three-layer composite.

EXAMPLE II The procedure of EXAMPLE I is repeated using the thicknessesand oxides summarized in the TABLE I hereinafter. All of the thicknessesare in angstrom units.

Subsequent sealing of glass substrates coated with each combinationdemonstrates the thermal stability of each three-layer composite.

We claim:

1. In a process for manufacturing a gaseous discharge display/memorydevice containing dielectric charge storage members, the improvementwhich comprises thermally evaporating and depositing a three-layercomposite on the charge storage surface of each dielectric member; thefirst layer consisting of at least one compound of Group IIA, Al, Si,Ti, Zr, I-lf, or mixtures thereof; the second layer consisting of atleast one compound of Group IIA, Al, Si, Ti, Zr, Hf, or mixtures thereofwhich is chemically different from the first layer; and the third layerconsisting of an electronemissive material; the combination of the firstand second layers being sufficient to prevent ion migration from thedielectric to the third layer and sufficient to provide a thermally andstructurally stable base for such third layer; and the second layerbeing chemically inert relative to the third layer.

2. The process of claim 1 wherein each layer is applied by means ofelectron beam evaporation.

3. The process of claim 1 wherein each dielectricmember is heated to atemperature of about 150F to about 600F and the three-layer compositeapplied thereto.

4. The process of claim 1 wherein the thickness of each layer is about200 angstrom units to about l0,000 angstrom units.

5. The process of claim 1 wherein the third layer is selected from GaAs,GaP, lnAs, InSb, InP, NiO, AgOCs, and AuOCs.

6. The process of claim 1 wherein all three layers are oxides.

7. The process of claim 6 wherein the third layer is selected frommagnesium oxide and lead oxide.

8. The process of claim ll, wherein the compounds of the first andsecond layers are selected from oxides.

9. The process of claim 8, wherein the third layer is selected from CsF,CsI, lead oxide and magnesium oxide.

10. The process of claim 1 wherein the thickness of each layer is atleast angstrom units.

11. The process of claim 10, wherein said first, second, and thirdlayers are silica, aluminum oxide and lead oxide respectively.

12. The process of claim 10, wherein said first, second, and thirdlayers are silica, zirconium oxide, and lead oxide respectively.

13. The process of claim 10, wherein said first, second, and thirdlayers are magnesium oxide, zirconium oxide, and lead oxiderespectively.

14. The process of claim 10, wherein said first, second, and thirdlayers are Si N silica, and lead oxide respectively.

15. The process of claim 10, wherein said first, second, and thirdlayers are magnesium oxide, aluminum oxide, and lead oxide respectively.

16. The process of claim 10, wherein said first, second, and thirdlayers are silica, aluminum oxide, and magnesium oxide respectively.

17. The process of claim 10 wherein said first, second, and third layersare silica, zirconium oxide, and magnesium oxide respectively.

18. The process of claim wherein said first, second, and third layersare magnesium oxide, zirconium oxide, and magnesium oxide respectively.

19. The process of claim 10 wherein said first, second, and third layersare Si N silica, and magnesium oxide respectively.

20. The process of claim 10 wherein said first, second, and third layersare magnesium oxide, aluminum oxide, and magnesium oxide respectively.

21. In a process for manufacturing a gaseous discharge display/memorydevice wherein an array of electrodes is applied to a glass substrateand a dielectric layer is applied over the electrodes, and wherein apair of glass substrates are sealed, dielectric to dielectric, to form achamber which is filled with an ionizable gas, the improvement whichcomprises electron beam evaporating and depositing upon the surface ofeach dielectric a three-layer composite; the first layer consisting ofat least one compound of Group IIA, Al, Si, Ti, Zr, Hf, or mixturesthereof; the second layer consisting of at least one compound of GroupIIA, Al, Si, Ti, Zr, Hf, or mixtures thereof which is chemicallydifferent from the first layer; and the third layer consisting of anelectronemissive material; the combination of the first and secondlayers being sufficient to prevent ion migration from the dielectric tothe third layer and sufficient to provide a thermally and structurallystable base for the third layer; and the second layer being chemicallyinert relative to the third layer.

22. The process of claim 21 wherein a sealing composition is applied tothe perimeter of each substrate prior to the applying of the composite.

23. The process of claim 21 wherein the thickness of each layer is atleast 100 angstrom units.

24. The process of claim 21 wherein the thickness of each layer is about200 angstrom units to about 10,000 angstrom units.

25. The process of claim 21 wherein the third layer is selected fromGaAs, GaP, InAs, InSb, InP, NiO, AgOCs, and AuOCs.

26. The process of claim 21 wherein said first, second, and third layersare silica, aluminum oxide and ond, and third layers are Si ,N,,,silica, and lead oxide respectively.

30. The process of claim 21 wherein said first, second, and third layersare magnesium oxide, aluminum oxide, and lead oxide respectively.

31. The process of claim 21 wherein said first, second and third layersare silica, aluminum oxide, and magnesium oxide respectively.

32. The process of claim 21 wherein said first, second and third layersare silica, zirconium oxide, and magnesium oxide respectively.

33. The process of claim 21 wherein said first, second, and third layersare magnesium oxide, zirconium oxide, and magnesium oxide respectively.

34. The process of claim 21 wherein said first, second, and third layersare Si N silica, and magnesium oxide.

35. The process of claim 21 wherein said first, second, and third layersare magnesium oxide, aluminum oxide, and magnesium oxide respectively.

36. The process of claim 22 wherein each layer is applied while eachsubstrate is at a temperature of about F to about 600F.

37. The process of claim 36 wherein the first layer is magnesium oxide,the second layer is aluminum oxide, and the third layer is selected frommagnesium oxide or lead oxide.

38. The process of claim 21 wherein the compounds of the first andsecond layers are selected from oxides.

39. The process of claim 38 wherein the third layer is selected fromCsF, Csl, lead oxide and magnesium

2. The process of claim 1 wherein each layer is applied by means ofelectron beam evaporation.
 3. The process of claim 1 wherein eachdielectric member is heated to a temperature of about 150*F to about600*F and the three-layer composite applied thereto.
 4. The process ofclaim 1 wherein the thickness of each layer is about 200 angstrom unitsto about 10,000 angstrom units.
 5. The process of claim 1 wherein thethird layer is selected from GaAs, GaP, InAs, InSb, InP, NiO, AgOCs, andAuOCs.
 6. The process of claim 1 wherein all three layers are oxides. 7.The process of claim 6 wherein the third layer is selected frommagnesium oxide and lead oxide.
 8. The process of claim 1, wherein thecompounds of the first and second layers are selected from oxides. 9.The process of claim 8, wherein the third layer is selected from CsF,CsI, lead oxide and magnesium oxide.
 10. The process of claim 1 whereinthe thickness of each layer is at least 100 angstrom units.
 11. Theprocess of claim 10, wherein said first, second, and third layers aresilica, aluminum oxide and lead oxide respectively.
 12. The process ofclaim 10, wherein said first, second, and third layers are silica,zirconium oxide, and lead oxide respectively.
 13. The process of claim10, wherein said first, second, and third layers are magnesium oxide,zirconium oxide, and lead oxide respectively.
 14. The process of claim10, wherein said first, second, and third layers are Si3N4, silica, andlead oxide respectively.
 15. The process of claim 10, wherein saidfirst, second, and third layers are magnesium oxide, aluminum oxide, andlead oxide respectively.
 16. The process of claim 10, wherein saidfirst, second, and third layers are silica, aluminum oxide, andmagnesium oxide respectively.
 17. The process of claim 10 wherein saidfirst, second, and third layers are silica, zirconium oxide, andmagnesium oxide respectively.
 18. The process of claim 10 wherein saidfirst, second, and third layers are magnesium oxide, zirconium oxide,and magnesium oxide respectively.
 19. The process of claim 10 whereinsaid first, second, and third layers are Si3N4, silica, and magnesiumoxide respectively.
 20. The process of claim 10 wherein said first,second, and third layers are magnesium oxide, aluminum oxide, andmagnesium oxide respectively.
 21. In a process for manufacturing agaseous discharge display/memory device wherein an array of electrodesis applied to a glass substrate and a dielectric layer is applied overthe electrodes, and wherein a pair of glass substrates are sealed,dielectric to dielectric, to form a chamber which is filled with anionizable gas, the improvement which comprises electron beam evaporatingand depositing upon the surface of each dielectric a three-layercomposite; the first layer consisting of at least one compound of GroupIIA, Al, Si, Ti, Zr, Hf, or mixtures thereof; the second layerconsisting of at least one compound of Group IIA, Al, Si, Ti, Zr, Hf, ormixtures thereof which is chemically different fRom the first layer; andthe third layer consisting of an electron-emissive material; thecombination of the first and second layers being sufficient to prevention migration from the dielectric to the third layer and sufficient toprovide a thermally and structurally stable base for the third layer;and the second layer being chemically inert relative to the third layer.22. The process of claim 21 wherein a sealing composition is applied tothe perimeter of each substrate prior to the applying of the composite.23. The process of claim 21 wherein the thickness of each layer is atleast 100 angstrom units.
 24. The process of claim 21 wherein thethickness of each layer is about 200 angstrom units to about 10,000angstrom units.
 25. The process of claim 21 wherein the third layer isselected from GaAs, GaP, InAs, InSb, InP, NiO, AgOCs, and AuOCs.
 26. Theprocess of claim 21 wherein said first, second, and third layers aresilica, aluminum oxide and lead oxide respectively.
 27. The process ofclaim 21 wherein said first, second, and third layers are silica,zirconium oxide, and lead oxide respectively.
 28. The process of claim21 wherein said first, second, and third layers are magnesium oxide,zirconium oxide, and lead oxide respectively.
 29. The process of claim21 wherein said first, second, and third layers are Si3N4, silica, andlead oxide respectively.
 30. The process of claim 21 wherein said first,second, and third layers are magnesium oxide, aluminum oxide, and leadoxide respectively.
 31. The process of claim 21 wherein said first,second and third layers are silica, aluminum oxide, and magnesium oxiderespectively.
 32. The process of claim 21 wherein said first, second andthird layers are silica, zirconium oxide, and magnesium oxiderespectively.
 33. The process of claim 21 wherein said first, second,and third layers are magnesium oxide, zirconium oxide, and magnesiumoxide respectively.
 34. The process of claim 21 wherein said first,second, and third layers are Si3N4, silica, and magnesium oxide.
 35. Theprocess of claim 21 wherein said first, second, and third layers aremagnesium oxide, aluminum oxide, and magnesium oxide respectively. 36.The process of claim 22 wherein each layer is applied while eachsubstrate is at a temperature of about 150*F to about 600* F.
 37. Theprocess of claim 36 wherein the first layer is magnesium oxide, thesecond layer is aluminum oxide, and the third layer is selected frommagnesium oxide or lead oxide.
 38. The process of claim 21 wherein thecompounds of the first and second layers are selected from oxides. 39.The process of claim 38 wherein the third layer is selected from CsF,CsI, lead oxide and magnesium oxide.